Issue ImGui API calls inside app render pass

Author: karnkaul

guide/src/dear_imgui/imgui_integration.md

@@ -33,9 +33,15 @@ Start a new ImGui frame after resetting the render fence, and show the demo wind
 m_device->resetFences(*render_sync.drawn);
 m_imgui->new_frame();
 
+// ...
+render_sync.command_buffer.beginRendering(rendering_info);
 ImGui::ShowDemoWindow();
+// draw stuff here.
+render_sync.command_buffer.endRendering();
 ```
 
+ImGui doesn't draw anything here (the actual draw command requires the Command Buffer), it's just a good customization point to use indirection at later.
+
 We use a separate render pass for Dear ImGui, again for isolation, and to enable us to change the main render pass later, eg by adding a depth buffer attachment (`DearImGui` is setup assuming its render pass will only use a single color attachment).
 
 ```cpp

src/app.cpp

@@ -183,8 +183,6 @@ void App::main_loop() {
 		m_device->resetFences(*render_sync.drawn);
 		m_imgui->new_frame();
 
-		ImGui::ShowDemoWindow();
-
 		auto command_buffer_bi = vk::CommandBufferBeginInfo{};
 		// this flag means recorded commands will not be reused.
 		command_buffer_bi.setFlags(
@@ -222,6 +220,7 @@ void App::main_loop() {
 			.setLayerCount(1);
 
 		render_sync.command_buffer.beginRendering(rendering_info);
+		ImGui::ShowDemoWindow();
 		// draw stuff here.
 		render_sync.command_buffer.endRendering();